This invention relates to multifunctional fibrous structures containing particles, which are useful in the manufacture of disposable diapers, adult incontinence pads, sanitary napkins and the like, scrubbing pads, scouring pads and cleaning pads that contain a detergent or soap and the like, and pads that contain coffee, tea, and the like. More particularly, the invention is directed to fibrous articles having sealed lateral edges to contain fibers and particles within the structure.
Fibrous structures may be used as absorbent articles, cleaning pads containing a detergent, coffee or tea bags.
Absorbent articles such as disposable diapers, adult incontinence pads, sanitary napkins, panty liners and the like, are generally provided with an absorbent core to receive and retain bodily liquids. The absorbent core is usually sandwiched between a liquid pervious top sheet, whose function is to allow the passage of fluid to the core, and a liquid impervious backsheet, whose function is to contain the fluid and to prevent it from passing through the absorbent article to the garment of the wearer of the absorbent article.
An absorbent core for diapers and adult incontinence pads frequently includes fibrous batts or webs constructed of defiberized, loose, fluffed, hydrophilic, cellulosic fibers. The core may also include a layer or stratum containing superabsorbent polymer (SAP) particles, granules, flakes or fibers, often referred to as the storage layer or stratum.
In recent years, market demand for an increasingly thinner and more comfortable absorbent article has increased. Such an article may be obtained by decreasing the thickness of the diaper core, by reducing the amount of fibrous material used in the core while increasing the amount of SAP particles, and by calendering or pressing the core to reduce caliper and hence, increase density.
Such higher density cores do not absorb liquid as rapidly as lower density cores because the compacting of the core (densification) results in smaller effective pore size. Accordingly, to maintain suitable liquid absorption, it is necessary to provide a lower density layer having a larger pore size above the highdensity absorbent core to increase the rate of uptake of liquid discharged onto the absorbent article. The low-density layer is typically referred to as an acquisition layer. Multiple layer absorbent core designs involve a more complicated manufacturing process.
The storage layer portion of a disposable diaper for example, is generally formed in place, during the converting process, from loose, fluffed cellulose. Such cellulose material is generally not available in preformed roll form because it exhibits insufficient web strength, owing to its lack of interfiber bonding or entanglement, to be unwound directly onto and handled in absorbent pad-making equipment.
Ultra-thin feminine napkins are generally produced from roll-goods based nonwoven material. Such a roll of preformed absorbent core material is unwound directly onto the absorbent article converting equipment without the defiberization step required for fluff-based products, such as diapers and incontinence pads. The nonwoven web is typically bonded or consolidated in a fashion that gives it sufficient strength to be handled in the converting process. These webs may also contain SAP particles.
The web consolidation mechanisms used in the roll-goods approach to making preformed cores provide strength and dimensional stability to the web. Such mechanisms include latex bonding, bonding with thermoplastic or bicomponent fibers or, thermoplastic powders, hydroentanglement, needlepunching, carding or the like. At high particle loading, however, the core structures exhibit poor particle containment. In other words, some of the particles tend to escape from the structure during manufacture, handling, shipping and converting and in use. This can result in the fouling of manufacturing and converting equipment as well as negative consumer perception of the product.
There is a need for an absorbent core material which facilitates fluid transport from an acquisition zone to a storage zone, exhibits good particle containment at high particle loading, is thin but has a high absorbent capacity in use, and can be delivered in roll-goods form to simplify the manufacturing and converting processes.
It is an object of the invention to provide a fibrous web comprising functional particles, which can be formed into absorbent articles containing functional particles having improved properties of particle containment and reduced amounts of delamination and powder spillage.
It is an object of the invention to provide a method of forming an edge seal in a fibrous article, to provide improved containment of functional particles which are present in the absorbent article.
It is another object of the invention to provide an improved method of disposing functional particles in a fibrous absorbent article, to provide an effective absorbent article having improved properties of strength and particle containment, and reduced amounts of particle spillage.
It has now been surprisingly and unexpectedly discovered that a fibrous article containing functional particles can be made with an air laid process using certain binders to facilitate strong edge seals, without the loss of functional particles through powder spillage.
In a first embodiment, the invention is directed to a fibrous web which comprises a lower stratum comprising matrix fibers and a thermoplastic bonding material; and an upper stratum comprising matrix fibers and a thermoplastic bonding material. The web further comprises a plurality of functional particle areas which are positioned between the upper and lower strata so as to contact each of the upper and lower strata. The functional particle areas are separated from other functional particle areas by a particle-free seal area comprising a seal formed between the upper and lower strata.
The seal area may be formed by compacting (densification) the upper and lower strata, for example by the application of pressure or heat. Alternatively, and or additionally, a binder may be applied to the seal area. Upon curing, the binder will serve to aid in the sealing of the upper and lower strata at the seal area.
In preferred embodiments, the seal area is substantially free of functional particles. in another embodiment, the invention is directed to a fibrous structure containing lower and upper strata comprising matrix fibers and optionally a thermoplastic bonding material; a functional particle area positioned between the upper and lower strata so as to contact each of the upper and lower strata; and a seal area comprising a seal formed between the upper and lower strata, wherein the seal area is substantially free of functional particles. In preferred embodiments, the fibrous article has at least two seal areas, wherein the seal areas are disposed on opposing edges of the article. The fibrous structure may be disposed as an absorbent core in a product, such as a disposable diaper, adult incontinence pad, sanitary napkin and the like. Alternatively, the fibrous structure can be used as a pad that contains coffee, tea, and the like, or a scrubbing pad, scouring pad and cleaning pad that contains a detergent or soap and the like.
In preferred embodiments, the upper and lower strata comprise cellulosic or synthetic fibers and a thermoplastic bonding material, such as bicomponent fibers; and the particle area includes particles such as super absorbent polymers (SAP), and odor control agents, such as zeolite or calcium carbonate.
In one embodiment, the invention is directed to an absorbent article (such as a diaper, sanitary napkin, or adult incontinence garment) which contains a fluid pervious topsheet; a fluid impervious backsheet; and an absorbent core disposed therebetween, wherein the absorbent core comprises a first stratum which contains matrix fibers and a thermoplastic bonding material and a second stratum which contains matrix fibers and a thermoplastic bonding material; and wherein one of the first or second strata is in fluid contact with the fluid pervious topsheet or the fluid impervious backsheet. Functional particles are disposed between the second and third strata. In addition, a seal area is formed between the second and third strata, wherein the seal area is substantially free of functional particles.
In still another embodiment, the invention is directed in part to a process for making an airlaid unitary fibrous structure, such as a fibrous web or absorbent core of the type described above. The process includes the steps of:
(a) providing a first stratum of a fibrous web;
(b) positioning functional particles in a first area on the first stratum;
(c) providing a second stratum of a fibrous web;
(d) positioning the second stratum on the first stratum so as to contact the first stratum and the particles;
(e) sealing the first and second strata at the non-particle area, thereby forming a discrete particle area positioned between the upper and lower strata; and
(f) curing the structure at a temperature of from 125 to 180xc2x0 C.
The process of the invention may also include the use of a binder. In a first application, a binder may be applied to the web so as to contact an area of the web which is free of particles, in order to strengthen the seal area. Additionally, the process of the invention may also include the steps of applying a second binder to the upper and lower strata to minimize dust off and to immobilize the particles contained in the structure; and (h) curing the structure at a temperature of from 125 to 1 80xc2x0 C.
In particular embodiments, the invention is directed to methods of making absorbent structures.